Retinal ischemia is implicated in the pathogenesis of vascular proliferation in retinal vascular disorders such as diabetic retinopathy and branch vein occlusion (BVO). Currently, ischemia is defined as capillary non-perfusion as seen on a fluorescein angiogram, but it is not clear whether there may be varying degrees of ischemia within areas of non-perfusion. Although this and other pre-proliferative signs help to identify diabetics at risk for developing neovascularization (NV), only about 50% of BVO patients with extensive fluorescein capillary non-perfusion develop NV. A predominant hypothesis for explaining the relationship between ischemic retina and NV states that ischemic, but still viable retina manufactures an "angiogenesis factor" which stimulates the growth of new vessels. This hypothesis suggests that if abnormal retinal function accompanying ischemia can be measured, then it may be possible to segregate patients on the basis of retinal function into prognostic groups. Preliminary psychophysical data indicate that thresholds are elevated in areas of capillary non-perfusion. Furthermore, threshold elevations in BVO patients who have developed NV appear to be different from those who have not developed NV. Likewise, the sensitivity of the electroretinogram (ERG) (as determined by an intensity-response function) appears to be different in the 2 types of patients, even though the single flash ERG may look normal. The proposed research will use these psychophysical and electrophysiologic measures to study visual function deficits due to ischemia in patients with diabetic retinopathy and branch vein occlusion. The data will be compared to fluorescein angiograms to document the severity of the vascular pathology, and to establish the degree of correspondence with areas of capillary non-perfusion. To determine whether these data measures have any capacity to differentiate among patients having different prognoses, a discriminant function analysis will be performed. The purpose of this study is to identify factors which monitor the extent of retinal ischemia, and thereby may serve as sensitive predictors of NV.